Treatment of background areas of developed electrophotographic elements with carboxy substituted triarylamine photoconductors with an alkaline medium to reduce opacity

ABSTRACT

ELECTROPHOTOGRAPHIC ELEMENTS HAVING LOW OPTICAL OPACITY ARE PREPARED BY SUBJECTING A DEVELOPED IMAGE-BEARING ELEMENT TO AN ALKALINE MEDIUM.

United States Patent 01 fice US. Cl. 96-1 13 Claims ABSTRACT OF THE DISCLOSURE Electrophotographic elements having low optical opacity are prepared by subjecting a developed image-bearing element to an alkaline medium.

This invention relates to electrophotography and more particularly to a method for producing by an electrophotographic process an element having improved reprint properties.

The process of xerography, as disclosed by Carlson in US. 2,297,691, employs an electrophotographic element comprising a support material bearing a coating of a normally insulating material Whose electrical resistance varies with the amount of incident actinic radiation it receives during an imagewise exposure. The element, commonly termed a photoconductive element, is first given a uniform surface charge, generally in the dark after a suitable period of dark adaptation. It is then exposed to a pattern of actinic radiation which has the effect of differentially reducing the potential of this surface charge in accordance with the relative energy contained in various parts of the radiation pattern. The differential surface charge or electrostatic latent image remaining on the electrophotographic.

element is then made visible by contacting the surface with a suitable electroscopic marking material.-Such marking material or toner, whether contained in an insulating liquid or on a dry carrier, can be deposited on the exposed surface in accordance with either the charge pattern or in the absence of charge pattern as desied. Deposited marking material can then be either permanently fixed to thesurface of the sensitive element by known means such as heat, pressure, solvent vapor, or the like, or transferred to a second element to which it can similarly be fixed. Likewise, the electrostatic latent image can be transferred to a second element and developed there.

While photoconductor-containing electrophotographic elements have a wide range of utilities, an application in which they are finding increasing utility is the recording of data presented on cathode-ray tube screens and the like. Advantages gained through such use include attractively high photographic speed, desirable spectral response, and short time of access to a visible recorded image.

It is frequently desirable to employ the image-bearing electrophotographic element as a master from which further prints can be generated. Such elements can be used as masters in many types of reproduction processes. Typical of these processes are the xerographic process, thermographic process, direct electrostatic process, stabilization process, gelatin transfer process, diffusion transfer process, etc. A particularly advantageous process by which such a print can be made is the diazo process. In this process, a diazonium salt-containing element is exposed through a transparent original bearing an image to activating radiation from an ultraviolet source. The exposure causes decomposition of the salt in those areas which are struck by activating radiation. Subsequently, the element is passed through an atmosphere of a suitable 3,585,026 Patented June 15, 1971 alkaline material, such as ammonia vapor. In the presence of the alkaline material and a dye-forming coupler, which may be either incorporated in the diazonium-containing layer or introduced during the development step, the diazonium salt which is not decomposed by exposure is converted to an azo dye. A positive reproduction of the original is formed.

A difficulty commonly encountered in the production of copies from sensitized photoconductor-containing coated elements is that the photoconductive element possesses a relatively high optical opacity resulting from coloration imparted by the photoconductive composition. As a result the element does not transmit suflicient radiation in that portion of the electromagnetic spectrum to which the copy element is sensitive. Therefore, reprints are very difficult to obtain. Also, if the image-bearing elements are to be used for direct reading, the image portions of the elements are often almost indiscernible due to the lack of contrast. There is thus seen to be a need for a method of increasing the radiation-transmitting capability of organic photoconductor-containing elements in the various regions of the electromagnetic spectrum.

It is therefore an object of this invention to provide a process for improving the reprint contrast of image-bearing photoconductor-containing electrophotographic elements.

It is another object of this invention to provide a novel process for producing a visible image using an electrophotographic element containing an organic photoconductor.

These and other objects of this invention are accomplished by decreasing the optical opacity in non-image areas of image-bearing electrophotographic elements containing certain organic photoconductors and sensitizers by subjecting the elements to an alkaline medium for a period of time following conventional exposure and development. The class of organic photoconductors amenable to this process include those triarylamines which are substituted by at least one radical having a carboxy group or by a group which is convertible to a carboxy group under the conditions at which the steps of the novel process are carried out. -As herein used, the term carboxy group includes those groups which are convertible to a carboxy group under the conditions described above. Typical groups which can be substituted on the triarylamine moiety include: a carboxy radical, a carboxy anhydride radical, an alkylene carboxy radical having 1 to 18 carbon atoms, an arylene carboxy radical including substituted arylene carboxy radicals (e.g.,

wherein D and E are phenyl or lower alkyl radicals) and and a vinylene carboxy radical, e. g.

wherein n is an integer from one to three.

The preferred organic photoconductors for use in the process of this invention are triarylamines having the following structure:

COOH

(2) Ar is an arylene radical including a substituted arylene radical such as a phenylene radical or a naphthylene radical; and

(3) X is a radical having a carboxy group.

Some typical photoconductors which are useful in this invention include:

N,N-diphenylanthranilic acid, Bis(p-diphenylaminobenzal)succinic acid, 4-carboxytriphenylamine, 3-(p-diphenylaminophenyl)-2-butenoic acid, 4-vinyl-4-diphenylaminocinnamic acid, 4-N,N-bis (p-bromophenyl) aminocinnamic acid, di-diphenylaminophenylpentadienoic acid,

1- (4-diphenylamino naphthacrylic acid, p-diphenylamino-a-cyanocinnamic acid, 3-p-diphenylaminophenylpropionic acid, p-diphenylaminocinnamic acid, 2,6-diphenyl-4-(p-diphenylaminophenyl)benzoic acid, p-diphenylaminophenylheptatrienoic acid, and p-diphenylaminocinnamic acid anhydride.

Other useful organic photoconductors are described in two copending applications by Brantly, Contois and Fox both entitled Photoconductive Elements Containing Organic Photoconductors, Ser. Nos. 706,780 and 706,800, both filed Feb. 20, 1968. These compounds can be prepared by the methods set forth in a copending application by Brantly and Fox entitled Novel Substituted Triarylamines, Ser. No. 706,799, filed Feb. 20, 1968.

Electrophotographic elements of the invention can be prepared with these photoconducting compounds in the usual manner, i.e., by blending a dispersion or solution of a photoconductive compound together with a binder, when necessary or desirable, and coating or forming a self-supporting layer with the photoconductor-containing material. Mixtures of the photoconductors described herein can be employed. Likewise, other photoconductors known in the art can be combined with the present photoconductors. In addition, supplemental materials useful for changing the spectral sensitivity or electrophotosensitivity of the element can be added to the composition of the element when it is desirable to produce the characteristic effect of such materials.

Generally, the photoconducting compounds of this invention are not sensitive to light unless a sensitizing compound is present.

It has been found that pyrylium salts, that is the pyrylium, thiapyrylium and selenapyrylium salts of U.S. Patent 3,250,615, are particularly useful for sensitizing these compounds to the extent that they exhibit relatively high electrical speeds compared to those compounds which do not have an active hydrogen-containing group. Other sensitizing compounds useful with the photoconductors of the invention include fluorenes, such as 7,12-dioxo-13-didibenzo(a,h) fluorene, 5,10-dioxo-4a,11-diazabenzo(b)- fiuorene, 3,13-dioxo-7-oxadibenzo(b,g)fiuorene, trinitrofiuorenone, tetranitrofluorenone and the like; aromatic nitro compounds of U.S. Pat. 2,610,120; anthrones of U.S. Pat. 2,670,285; quinones of U.S. Pat. 2,670,286; benzophenones of U.S. Pat. 2,670,287; thiazoles of U.S. Pat. 2,732,301; mineral acids; carboxylic acids, such as maleic acid, dichloroacetic acid, and salicyclic acid; sulfonic and phosphoric acids; and various dyes such as triphenylmethane, diarylmethane, thiazine, azine, oxazine, xanthene, phthalein, acridine, azo, anthraquinone dyes, and many other suitable sensitizing dyes such as the cyanine, merocyanine and azacyanine dyes of U.S. Ser. No. 633,421, filed Apr. 25, 1967, now abandoned. The preferred sensitizers for use in elements suitable for the process of this invention are pyrylium and thiapyrylium dye salts and the cyanine and related dyes of the above mentioned U.S. Ser. No. 633,421, now abandoned.

In preparing the photoconducting layers disclosed herein, it is conventional practice to mix a suitable amount of the sensitizing compounds with the coating composition so that, after thorough mixing, the sensitizing compound is uniformly distributed throughout the desired layer of the coated element. The amount of sensitizer that can be added to a photoconductor-incorporating layer to give effective increases in speed can vary widely. The optimum concentration in any given case will vary with the specific photoconductor and sensitizing compound used. In general, substantial speed gains can be obtained where an appropriate sensitizer is added in a concentration range from about 0.0001 to about 30 percent by weight based on the weight of the film-forming photoconductive composition. Generally, a sensitizer is added to the coating composition in an amount from about 0.005 to about 5.0 percent by weight of the total coating composition.

Preferred binders for use in preparing the present photoconductive layers are film-forming polymeric binders having fairly high dielectric strength which are good electrically insulating film-forming vehicles. Materials of this type comprise styrene-butadiene copolymers; silicone resins; styrene-alkyd resins; silicone-alkyd resins; soyaalkyd resins; poly(vinyl chloride); poly(vinylidene chloride); vinylidene chloride-acrylonitrile copolymers; poly- (vinyl acetate); vinyl acetate-vinyl chloride copolymers; poly(vinyl acetals), such as poly(vinyl butyral); polyacrylic and methacrylic esters, such as poly(methylmethacrylate), poly(n-butylmethacrylate), poly(isobutyl methacrylate), etc.; polystyrene; nitrated polystyrene; polymethylstyrene; isobutylene polymers; polyesters, such as poly(ethylenealkaryloxyalkylene terephthalate); phenolformaldehyde resins; ketone resins; polyamides; polycarbonates; polythiocarbonates; poly(ethyleneglycol-co bishydroxyethoxy phenyl propane terephthalate); nuclear substituted vinyl haloarylates such as poly(vinyl metabromobenzoate-co-vinyl acetate); etc. Methods of making resins of this type have been described in the prior art, for example, styrene-alkyd resins can be prepared according to the method described in U.S. Pats. 2,361,019 and 2,258,423. Suitable resins of the type contemplated for use in the photoconductive layers of the invention are under such trade names as Vitel PE-lOl, Cymac, Piccopale 100, Saran F-220, and Lexan 105. Other types of binders which can be used in the photoconductive layers of the invention include such materials as paraffin, mineral waxes, etc.

Solvents of choice for preparing coating compositions of the present invention can include a number of solvents such as benzene, toluene, acetone, Z-butanone, chlorinated hydrocarbons, e.g., methylene chloride, ethylene chloride, etc., ethers, e.g., tetrahydrofuran, or mixtures of these solvents, etc.

In preparing the coating composition useful results are obtained where the photoconductor substance is present in an amout equal to at least about 1 Weight percent of the coating composition. The upper limit in the amount of photoconductor substance present can be widely varied in accordance with usual practice. In those cases where a binder is employed, it is normally required that the photoconductor substance be present in an amount from about 1 weight percent of the coating composition to about 99 weight percent of the coating composition. A preferred weight range for the photoconductor substance in the coating composition is from about 10 weight percent to about 60 weight percent.

Coating thicknesses of the photoconductive composition on a support can vary widely. Normally, a coating in the range of about 0.001 inch to about 0.01 inch before drying is useful for the practice of this invention. The preferred range of coating thickness has been found to be in the range from about 0.002 inch to about 0.006 inch before drying although useful results can be obtained outside of this range.

Suitable supporting materials for coating the photoconductive layers of the present invention can include any of a Wide variety of eletcrically conducting supports, for example, paper (at a relative humidity above 20 percent); aluminum-paper laminates; metal foils such as aluminum foil, Zinc foil etc.; metal plates, such as aluminum, copper, zinc, brass, and galvanized plates; vapor deposited metal layers such as silver, nickel, or aluminum and the like. Metal (e.g., nickel, etc.) conducting layers deposited by high vacuum deposition techniques can be coated at lower coverages so as to be substantially transparent to facilitate image exposure through the support. An especially useful transparent conducting support can be prepared by coating a support material such as polyethylene terephthalate with a layer containing a semiconductor dispersed in a resin. Suitable conducting layers both with and without insulating barrier layers are described in US. Pat. 3,245,833. Other suitable conducting layers are described in US. Pat. 3,120,028. Likewise, a suitable conducting coating can be prepared from the sodium salt of a carboxyester lactone of maleic anhydride and a vinyl acetate polymer. Such kinds of conducting layers and methods for their optimum preparation and use are disclosed in US. Pats. 3,007,901 and 3,267,807.

The above described elements can be employed in any of the well-known electrophotographic processes which require photoconductive layers. One such process is the aforementioned xerographic process. As previously explained, in a process of this type the electrophotographic element is given a blanket electrostatic charge by placing the same under a corona discharge which serves to give a uniform charge to the surface of the photoconductive layer. This charge is retained by the layer owing to the substantial insulating property of the layer, i.e., the low conductivity of the layer in the dark. The electrostatic charge formed on the surface of the photoconducting layer is then selectively dissipated from the surface of the layer by exposure to light through an image-bearing transparency by a conventional exposure operation such as, for example, by contact-printing technique, or by lens projection of an image, etc., to form a latent image in the photoconducting layer. Another exposure technique involves exposing the charged electrophotographic element to the fluorescent pattern produced by a phosphor-coated inner surface of a cathode ray tube. The element can either be placed in direct contact with the cathode ray tube or the pattern produced on the inner surface of the tube can be transmitted to the element by fiber-optic techniques such as by employing a fiber scope. By exposure of the surface in this manner, a charge pattern is created by virtue of the fact that light causes the charge to be conducted away in proportion to the intensity of the illumination in a particular area. The charge pattern remaining after exposure is then developed, i.e., rendered visible, by treatment with a medium comprising electrostatically attractable particles having optical density. The developing electrostatically attractable particles can be in the form of a dust, e.g., powder, pigment in a resinous carrier, i.e., toner, or a liquid developer may be used in which the developing particles are carried in an electrically insulat ing liquid carrier. Methods of development of these types are widely known and have been described in the patent literature in such patents, for example, as U.S. Pat. 2,297,691 and in Australian Pat. 212,315. In processes of electrophotographic reproduction such as in xerography, by selecting a developing particle which has as one of its components, a low-melting resin, it is possible to treat the developed photoconductive material with heat to cause the powder to adhere permanently to the surface of the photoconductive layer. Techniques of the type indicated are well known in the art and have been described in a number of US. and foreign patents, such as US. Pats. 2,297,691 and 2,551,582, and in RCA Review, vol. (1954), pages 469-484. ,When liquid developers are used, the element may be heated to remove the solvent.

According to this invention, the optical opacity of the non-image areas of the image-bearing electrophotographic element is reduced by subjecting the element to an alkaline medium. The alkaline medium can be in any physical state, i.e., solid, liquid, or gas. However, the latter two are preferred because of convenience of application to the element. The material can be an inorganic alkaline material such as the alkali metal hydroxide, ammonium hydroxide, ammonia, etc., as well as an organic amines including the straight and branched chain alkyl amines, e.g., n-dodecylamine, as well as aromatic amines, e.g., aniline and heterocyclic amines, e.g., pyridine.

In practicing this invention, it is evident that the conditions under which the photoconductor-containing element is introduced into the alkaline medium can be varied widely. For example, it is known that the rate of reaction depends on both the concentration of the medium and its temperatures. Useful results can be obtained when the temperature is from about 0 C. to about 150 C. The preferred range is, however, from about 10 C. to about 100 C. Likewise, the time of treatment by the alkaline medium can be varied within wide limits in accordance with the requirements of the system in use. For example, the time may be from about 0.1 second to about 100 seconds, with times of from 0.5 second to 50 seconds being preferred.

The concentration of alkaline medium can also be varied widely from about 0.01 mole per liter to about 100 moles per liter. The preferred concentration ranges are from about 0.1 mole per liter to 10 moles per liter. The parameters of time, temperature and concentration can be adjusted so that optimum reprint or readability characteristics are attained for a particular photoconductive element employed. Generally, the conditions are so selected that the optical opacity of non-image areas is decreased substantially and preferably by at least 25%.

'Electrophotographic materials according to the present invention can be applied to reproduction techniques wherein different kinds of radiations, i.e., electromagnetic radiations as well as nuclear radiations, can be used. For this reason, it is pointed out herein that although materials according to the invention are mainly intended for use in connection with methods comprising an exposure, the term electrophotography wherever appearing in the description and the claims, is to be interpreted broadly and understood to comprise both xerography and xeroradiography.

The following examples are included for a further understanding of the invention.

EXAMPLE 1 Organic photoconductors of the type described herein are separately incorporated into a coating dope having the following composition:

Organic photoconductor0.5 g.

Polymeric binder1.5 g.

ensitizer0.02 g.

Methylene chloride1l.7 ml.

The resulting compositions are handcoated at a Wet thickness of 0.004 inch on a subbed poly(ethylene terephthalate) support bearing a conductive layer prepared according to Trevoy US. Pat. 3,245,833. The coating blocks are dried at a temperature of 90 F. In a darkened room, the surface of each of the photoconductive layers so prepared is charged to a potential of about +600 volts under a corona charger. The layer is then covered with a transparent sheet bearing a pattern of opaque and light transmitting areas and exposed to the radiation from an incandescent lamp with an illumination intensity of about meter-candles for 12 seconds. The resulting electrostatic latent image is developed by conventional electrophotographic liquid developers (e.g., U.S. Pat. 2,970,674) and also by cascading over the surface of the layer a mixture of negatively charged black thermoplastic toner particles and glass beads. When the liquid developer is used, the element is heated to remove residual solvent. A reproduction of the pattern is obtained in each instance. To test the reprint capabilities of these image-bearing elements, a conventional diazo film (International Business Ma- 8 chines Type D-l) is exposed through these elements usple 1 except that prior to exposure in the diazo processor, ing as the light source the lamp from a diazo processor the elements are subjected to the ammonia vapors gen- (3M Pilmsort Processor). The exposure time is 30 secerated in the developing section of the processor. Upon onds. No visible image differentiation is obtained before development of the diazo film, a good image on a clear or after development of the diazo film as shown in the 5 background is obtained in each distance. next example. These photoconductive elements are then subjected to an ammonia atmosphere for approximately EXAMPLES 5-9 20 seconds and the reprint characteristics of the elements In order to demonstrate the reduction in the Optical K treiited are f g by exposigg g z E thlgugh opacity for various photoconductors obtainable by subt e e ements t e manner 6 a 10 jecting them to an alkaline medium, coating dopes having development of the diazo film a good image on a clear the follo o to I r r r nd background is obtained. The data for the various photo- Wmg-C 081 1 n a e epa ed a coated m the manner described in Example 1. conductors, binders and sensitizers used 18 set forth in the following Table I. The polymeric binders referred to are: Organlc P n r- .5 g.

PVmBBPoly(vinyl ineta-bromobenzoate-co-vinyl acefigg f g gi ggsji'g h tate) Vitel 101A polyester of terephthalic acid and a mix- The elements are then subjected to ammonia vapors for ture of ethylene glycol (1 part by weight) and 2,2-bisapproximately seconds. The optical opacity is meas- [4-(fi-hydroxyethyl)phenyl]propane (9 parts by ured before and after the ammonia treatment. In each Weight) manufactured by Goodyear Tire and Rubber 20 case a substantial reduction in the optical opacity is noted Co. as set forth in the following Table III.

TABLE III Percent Optical opacity Optical opacity reduction prior to NH; after NH; in optical Photoeonductor Binder treatment treatment opacity 4-carboxytriphenylamine. 2. 2 6 Diphenylanthranilic acid. 2. 2 4-vinyl-4-diphenylaminoc ei 1. 5 50 p-Diphenylaminoucyanocinnamic acid" 1 2 9 p-Diphenylaminocinnamic acid do. 25. 0 at 440 m 3. 3 at 440 mu. 8G. 8

The sensitizers referred to are: The invention has been described in detail with particular reference to certain preferred embodiments theregg i gii if 6 (4 amyloxystyryl) pyryl of, but it will be understood that variations and modifica- Chlom 3 triphenylimidazo [4 35 tions can be eifected Within the spirit and scope of the quinoxaline-3-indolocarbocyanine TABLE I Image reproduced Subjected on electrophototo alkaline Image lhotoconductor Binder Sensitizer graphic element medium reprinted Example:

1a p-Diphenylaminocinnan1ic acid. PVmBB 1b ..d0 PYmBB EXAMPLE 2 invention as described hereinabove and as defined in the Example 1 is repeated except the step of subjecting the appended claims. image-bearing electrophotographic element to ammonia I claim: vapors is omitted. As seen from Table II below, reprints 50 1. A process for producing a visible image by electrocould not be obtained due to the high optical opacity of photography using an electrophotographic element having the element. coated on an electrically conducting support a photocon- TABLE II Image reproduced Subjected on electrophototo alkaline Image Photoconductor Binder Sensltlzer graphic element medium reprinted A B A EXAMPLE 3 ductive composition comprsing an organic photoconduc- Example 1 is repeated except the image bearing e1eC tor which is a carboxy substituted triarylamine and a trophotographic elements are passed through a liquid alkapyrylium dye salt sensitizer for said photoconductor, which line medium comprising n-dodecylamine instead of am- 5 comprls'is f steps of! monia vapors. In each instance the elements exhibit good (a) charging the electrophotographic element, reprint characteristics and lower optical opacity. (b) imagewise exposing the charged electrophoto- EXAMPLE 4 graphic element and thereby discharging said electro photographic element in areas of exposure,

Example 1 is repeated except that the charged electrophotographic elements are exposed to the fluorescent pattern produced by a phosphor-coated inner surface of a graphlc Image to Produce a visible Image and there cathode ray tube. The pattern is transmitted to the surface after of the elements by means of a fiber scope. The elements sublectlng the developed electrophotogmphlc are then treated in the same manner described in Examment to an alkaline medium for a period sufficient to (0) developing the resultant recorded electrophotosubstantially reduce the optical opacity of the nonimage areas.

2. The process as defined in claim 1 wherein the photoconductor is a triarylamine substituted by at least one radical selected from the group consisting of a carboxy radical,

a carboxy anhydride radical,

an alkylene carboxy radical,

an arylene carboxy radical, and

a vinylene carboxy radical.

3. A process for producing a visible image by electrophotography using an electrophotograpic element having coated on a transparent conductive support a photoconductive composition comprising an organic photoconductor having the formula:

wherein:

(1) Ar, and Ar are phenyl radicals,

(2) Ar is selected from the group consisting of phenylene and naphthylene radicals,

(3) X is a carboxy group; the composition further comprises pyrylium dye salt sensitizer for said photoconductor, comprising the steps of:

(a) charging the electrophotograpic element,

(b) imagewise exposing the charged electrophotographic element and thereby discharging said electrophotographic element in areas of exposure,

(c) developing the resultant recorded electrophotographic image to produce a visible image, and thereafter (d) subjecting the developed electrophotographic element to ammonia vapors at a temperature from C. to about 150 C. for a period from about 0.1 second to about 100 seconds to substantially reduce the optical opacity of the nonimage areas.

4. The process as defined in claim 3 wherein step (d) is carried out for a period sufiicient to reduce the optical opacity of the electrtophotographic element by at least 25%.

5. The process as defined in claim 3 wherein X is a radical selected from the group consisting of a carboxy radical,

a carboxy anhydride radical,

an alkylene carboxy radical,

an arylene carboxy radical, and

a vinylene carboxy radical.

6. A process for producing a visible image by electrophotography using an electrophotographic element having coated on a transparent conductive support a photoconductive composition comprising from about to about 60% by weight of said composition of an organic photoconductor having the formula:

N-Ars-X wherein:

(1) Ar and Ar are phenyl radicals,

(2) Ar is selected from the group consisting of phenylene and naphthylene radicals,

(3) X is a carboxy group, about 0.005 to about 5.0% by weight of said composition of a pyrylium dye salt sensitizer and a polymeric film-forming binder for said photoconductor, which comprises the steps of:

(a) charging the electrophotographic element, (b) imagewise exposing the charged electrophoto- 10 graphic element and thereby discharging said electrophotographic element in areas of exposure,

(0) developing the resultant recorded electrophotographic image to produce a visible image, and thereafter ((1) subjecting the developed electrophotographic element to ammonia vapors at a temperature from about 10 C. to about C. for a period sulficient to reduce the optical opacity of non-image areas by at least 25%.

7. A process for producing a visible image by electrophotography using an electrophotograpic element having coated on a transparent conductive support a photoconductive composition comprising from about 10% to about 60% by weight of said composition of p-diphenylaminocinnamic acid as an organic photoconductor, about 0.005 to about 5.0% by weight of said composition of a sensitizer selected from the group consisting of pyrylium, thiapyrylium and selenapyrylium dye salts and a polymeric film-forming binder for said photoconductor, which comprises the steps of (a) charging the electrophotographic element,

(b) imagewise exposing the charged electrophotographic element and thereby discharging said electrophotographic element in areas of exposure,

(0) developing the resultant recorded electrophotographic image to produce a visible image, and thereafter (d) subjecting the developed electrophotographic element to ammonia vapors at a temperature from about 10 C. to about 100 C. for a period sufiicient to reduce the optical opacity of non-image areas by at least 25%.

8. The process as defined in claim 7 wherein the polymeric film-forming binder is a polymer of a nuclear substituted vinyl haloarylate.

9. The process as defined in claim 7 wherein the polymeric film-forming binder is a poly(ethylenealkaryloxyalkylene terephthalate).

10. The process as defined in claim 7 wherein the polymeric binder is poly(vinyl meta-bromobenzoate-co-vinyl acetate).

11. The process as defined in claim 7 wherein the polymeric binder is a polyester of terephthalic acid and a mixture of ethylene glycol and 2,2-bis(4-hydroxyethoxyphenyl) propane.

12. The process as defined in claim 7 wherein the transparent support comprises poly(ethylene terephthalate) having coated thereon a conducting layer comprising cuprous iodide.

13. The process as defined in claim 7 wherein the sensitizer is 2,4 bis(4-ethoxyphenyl)-6-(4-amyloxystyryl)- pyrylium fiuoroborate.

References Cited UNITED STATES PATENTS 3,250,614 5/ 1966 Eastman 961 3,418,115 12/1968 Menold et a1. 9689X FOREIGN PATENTS 1,253,676 1/ 1961 France 96--1.5

DONALD LEVY, Primary Examiner R. E. MARTIN, Assistant Examiner US. Cl. X.R. 

